Stabilized aqueous active silica solution, silica sol using same, and method for producing same

Abstract

A stabilized aqueous active silica solution including at least one stabilizing agent selected from an acid, potassium hydroxide, ammonia and an organic base, whose content is 0.167 to 10% by mass/SiO2 relative to solution. The acid is an inorganic or organic acid. The inorganic acid is sulfuric or nitric acid. The organic acid is citric acid. The base is an amine or quaternary ammonium hydroxide. The viscosity of the solution that has a SiO2 concentration of 2.8 to 3.3% by mass, measured by the Ostwald method at 23° C. within 3 hours after production, is 0.5 to 20 mPa·s. The viscosity of the solution measured after storage at 23° C. for 3 days is higher by 5.0 times or less than that of the solution measured within 3 hours. Also, a silica sol including silica particles having an average primary particle diameter of 5 to 300 nm.

1 . A stabilized aqueous active silica solution comprising at least one stabilizer A selected from the group consisting of an acid, potassium hydroxide, ammonia, and an organic base, wherein
 the amount of the stabilizer A is 0.167 to 10% by mass relative to the mass of SiO 2  contained in the aqueous active silica solution.   
     
     
         2 . The stabilized aqueous active silica solution according to  claim 1 , wherein the acid is an inorganic acid or an organic acid. 
     
     
         3 . The stabilized aqueous active silica solution according to  claim 2 , wherein the inorganic acid is sulfuric acid or nitric acid. 
     
     
         4 . The stabilized aqueous active silica solution according to  claim 2 , wherein the organic acid is citric acid. 
     
     
         5 . The stabilized aqueous active silica solution according to  claim 1 , wherein the organic base is an amine or a quaternary ammonium hydroxide. 
     
     
         6 . The stabilized aqueous active silica solution according to any one of  claims 1 to 5 , wherein the aqueous active silica solution having an SiO 2  concentration of 2.8 to 3.3% by mass exhibits a viscosity of 0.5 to 20 mPa·s as measured by the Ostwald method at 23° C. within three hours after production, and the viscosity of the aqueous active silica solution measured after storage at 23° C. for three days is 5.0 times or less the viscosity measured at 23° C. within three hours after production. 
     
     
         7 . A silica sol comprising silica particles that are a polycondensate of the active silica contained in the stabilized aqueous active silica solution according to any one of  claims 1 to 6 , wherein the silica particles have an average primary particle diameter of 5 to 300 nm. 
     
     
         8 . The silica sol according to  claim 7 , wherein the silica sol contains potassium ions and sodium ions, and, when the silica sol has an SiO 2  concentration of 20% by mass, the amount of potassium ions contained in the silica sol is 1,500 to 5,000 ppm, and the ratio of (potassium ion concentration by ppm)/(Na ion concentration by ppm) is 100 to 1,000. 
     
     
         9 . A production method for the silica sol according to  claim 7 or 8 , the production method comprising the following processes (a) and (b):
 process (a): a process including a step of incorporating, into an aqueous active silica solution (a0), at least one stabilizer A selected from the group consisting of an acid, potassium hydroxide, ammonia, and an organic base so that the amount of the stabilizer A is 0.167 to 10% by mass/SiO 2 , thereby preparing a stabilized aqueous active silica solution (a1), and a step of incorporating potassium hydroxide into the stabilized aqueous active silica solution (a1) or a silica sol containing silica particles having an average primary particle diameter of 5 to 90 nm so that the ratio by mole of SiO 2 /K 2 O is 1.5 to 20, thereby preparing the seed liquid (a2); and   process (b): a process of heating the seed liquid (a2) prepared in the process (a) at 90 to 150° C.   
     
     
         10 . The production method for the silica sol according to  claim 9 , wherein the aqueous active silica solution (a0) used in the process (a) is prepared through:
 a process (c1) of preparing an aqueous active silica solution by cation exchange of liquid glass,   a process (c2) of adding an acid to the aqueous active silica solution, and aging the aqueous active silica solution at a temperature of higher than 0° C. and lower than 40° C. for 1 to 30 hours, and   a process (c3) of subjecting the aged aqueous active silica solution to cation exchange and anion exchange, thereby preparing the aqueous active silica solution (a0).   
     
     
         11 . The production method for the silica sol according to  claim 10 , wherein, in the process (c2), the aqueous active silica solution exhibits a pH of 0.5 to 3.0 after addition of the acid, and the aqueous active silica solution (a0) prepared through the process (c3) exhibits a pH of more than 3.0 and 6.0 or less. 
     
     
         12 . The production method for the silica sol according to  claim 10 or 11 , wherein the acid used in the process (c2) is sulfuric acid. 
     
     
         13 . The production method for the silica sol according to any one of  claims 9 to 12 , wherein the process (b) further includes a process of adding, to the heated seed liquid (a2), a feed liquid (b1) stabilized by adding at least one stabilizer B selected from the group consisting of an acid, potassium hydroxide, ammonia, and an organic base to the aqueous active silica solution (a0) so that the amount of the stabilizer B is 0.167 to 10% by mass relative to the mass of SiO 2  contained in the aqueous active silica solution. 
     
     
         14 . The production method according to  claim 13 , wherein the stabilizer A is sulfuric acid, the agent for adjusting the ratio by mole of SiO 2 /K 2 O is potassium hydroxide, and the stabilizer B is sulfuric acid. 
     
     
         15 . The production method according to  claim 13 , wherein the stabilizer A is potassium hydroxide, the agent for adjusting the ratio by mole of SiO 2 /K 2 O is potassium hydroxide, and the stabilizer B is potassium hydroxide.